The present invention relates to a torque sensor for detecting in a non-contact manner an amount of a torque transmitted to a shaft.
According to a conventional method for detecting in a non-contact manner an amount of a torque transmitted to a shaft, a strain produced on the surface of the shaft by the torque is converted into a relative permeability variation of a soft magnetic alloy having magnetostriction which is fixed to the surface of the shaft, and this variation is detected as an inductance variation through a coil disposed at the periphery of the shaft. However, the torque sensor of this type has disadvantages that the output of the sensor is changed by the difference between amounts of thermal expansion of the shaft and the soft magnetic alloy. The magnitude of this change depends on the difference of the coefficient of linear thermal expansion between the shaft, and soft magnetic alloy.
Accordingly, it is necessary to modify the factors of temperature compensation etc., in accordance with the change of the coefficient of linear thermal expansion which is caused when the kind of the material forming the shaft is changed. Moreover, sensitivity is considerably lowered when a thermal strain equal to or more than 400.times.10.sup.-6 due to the difference in amounts of the thermal expansion between the shaft and the soft magnetic alloy is applied to a soft magnetic layer.